1. Field of the Invention
The present invention relates to a projection apparatus, for example, a data projection apparatus, and a projection method.
2. Description of the Related Art
Techniques have been proposed which are used for a projection apparatus including light emitting diodes (LEDs) as a light source, to enable the red, green, and blue light emitting diodes to be lit and dimmed and enable the temperatures of the R, G, and B light emitting diodes to be individually controlled to appropriately and smoothly adjust and maintain the brightness and light emission efficiency of a display screen in an image display section, while allowing power consumption to be easily reduced (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-181528).
A method of adjusting light emission duration and a method of adjusting light emission intensity are possible for techniques for dimming the light emitting diodes, serving as a light source, including the technique described in Jpn. Pat. Appln. KOKAI Publication No. 2005-181528.
The former method of adjusting the light emission duration of the light source needs to adjust time for which images are displayed by a light modulating element such as a liquid crystal display panel, Digital Micromirror Device (DMD) (registered trade mark), or the like which forms projection images, according to the adjusted light emission duration. In particular, gradation display requires very complicated control. Consequently, this method is not practicable.
Furthermore, the latter method of adjusting the light emission intensity may involve, for example, controlling the current through each of the light emitting diodes.
FIG. 9 shows that a white light emitting diode group also using a color wheel is used as a light source. In this case, dimming is performed such that luminance is 80% of a rated value for projection of a red (R) image, is equal to the rated value, that is, 100% of the rated value, for projection of a green (G) image, and is 60% of the rated value for projection of a blue (B) image.
FIG. 9(A) shows projection timings for each color image. FIG. 9(B) shows the light emission intensity of the white light emitting diode group. FIGS. 9(C) to 9(E) show how the white light emitting diode group is driven for each color image. Here, for simplification of description, the white light emitting diode group is assumed to be composed of a total of five light emitting diodes w1 to w5.
As shown in FIGS. 9(C) to 9(E), when a red (R) image, a green (G) image, and a blue (B) image are projected, the driving current supplied to the light emitting diodes w1 to w5 is adjusted such that the luminance is 80%, 100%, and 60% of the rated value, respectively. All the light emitting diodes w1 to w5 are driven by a driving current of the same magnitude so as to emit light. Thus, the number of diodes simultaneously lit is always a total number, that is, “5”.
As described above, if the driving current is adjusted in an analog manner, particularly when the current is reduced so as to provide a low luminance, a response time from the current state until the next desired emission luminance is obtained is disadvantageously increased.
For example, in FIG. 9(B), described above, no problem occurs when the emission luminance changes from 80% to 100%. However, both when the emission luminance changes from 60% to 80% and when the emission luminance changes from 100% to 60%, the response is delayed, thus hindering accurate gradation display.
In order to avoid a possible decrease in response speed based on the adjustment of the driving current, a method can be used which controls the number of light emitting diodes emitting light with a 100% luminance instead of adjusting the driving current for the individual light emitting diodes.
FIG. 10 shows that a white light emitting diode group also using a color wheel is used as a light source. In this case, dimming is performed based on the number of light emitting diodes emitting light such that luminance is 80% of a rated value for projection of a red (R) image, is equal to the rated value, that is, 100% of the rated value, for projection of a green (G) image, and is 60% of the rated value for projection of a blue (B) image.
FIG. 10(A) shows projection timings for each color image. FIG. 10(B) shows the light emission intensity of the white light emitting diode group. FIGS. 10(C) to 10(E) show how the white light emitting diode group is driven for each color image. Also in this case, the white light emitting diode group is assumed to be composed of a total of five light emitting diodes w1 to w5.
As shown in FIGS. 10(C) to 10(E), when a red (R) image, a green (G) image, and a blue (B) image are projected, the number of those of the light emitting diodes w1 to w5 which emit light is adjusted such that the luminance is 80%, 100%, and 60% of the rated value, respectively.
In FIG. 10(C), to allow the white light emitting diode group as a whole to provide an 80% luminance, four of the five light emitting diodes w1 to w5, that is, the light emitting diodes w1 to w4, are driven so as to emit light with a luminance accounting for 100% of the rated value, with the remaining one light emitting diode w5 totally prevented from being driven.
In FIG. 10(D), to allow the white light emitting diode group as a whole to provide a 100% luminance, all the five light emitting diodes w1 to w5 are driven so as to emit light with a luminance accounting for 100% of the rated value.
In FIG. 10(E), to allow the white light emitting diode group as a whole to provide a 60% luminance, three of the five light emitting diodes w1 to w5, that is, the light emitting diodes w1 to w3, are driven so as to emit light with a luminance accounting for 100% of the rated value, with the remaining two light emitting diodes w4 and w5 totally prevented from being driven.
If the number of light emitting elements emitting light is adjusted to obtain the currently required luminance as described above, all the elements to emit light are driven at the rated value. This prevents a sufficient response speed from being achieved.
In contrast, the light emission duration varies among the plurality of light emitting elements making up the light source. As a result, the lifetime of the light emitting element located at the position where the element is most frequency used disadvantageously corresponds directly to the lifetime of the light source section as a whole.